The methods herein relate generally to the field of crude oil or natural gas production from a subterranean formation by a well, and particularly to methods to increase recovery of crude oil and natural gas production from such a well using fluids comprising small particles in the submicron size range. “Subterranean formation” refers to a fundamental unit of lithostraitigraphy; it is a body of rock that is sufficiently distinctive and continuous that it can be mapped. A “reservoir” is a subterranean formation containing oil or gas; it is in a shape that will trap hydrocarbons and is covered by a relatively impermeable rock, known as a cap rock. As used herein, a “well” includes at least one wellbore, and can include a near-wellbore region of the formation that surrounds and is in fluid communication with the wellbore.
The general process of producing oil and gas by way of a well and the various well fluids used therein are described in the art, for example in U.S. Appl. 2012/0181029, which is incorporated by reference. Broadly speaking, producing hydrocarbons by means of a well includes as major stages drilling, perforating and completing, and (the actual) producing, where the last stage, producing, corresponds to or coincides with, or can even be directly termed, well intervention. Well intervention generally includes any operation carried out on a well during or at the end of its productive life that alters the state of the well or well geometry, provides well diagnostics, or manages the production of the well.
Drilling, completion, and intervention operations each can include various types of treatments that are commonly performed on a well or subterranean formation. Some treatments, for example fluid-loss control, can be used during any of drilling, completion, and intervention operations. While stimulation is a type of treatment performed during completion or intervention to enhance or restore the productivity of oil and gas from a well, and can fall into two main groups, hydraulic fracturing and matrix treatments, depending on whether the fracture pressure is above or below that the subterranean formation. There are other types of completion or intervention treatments, including for example gravel packing, consolidation, and control of excessive water production.
Treatments therefore constitute a dimension or array of operations that are orthogonal to the main phases of drilling, completion, and intervention in hydrocarbon production. They are related to these main stages, but are also independent in that they can be introduced during or between any of these stages to serve a particular related purpose or to enhance the basic purpose of each stage. A treatment thus is used for changing a condition of a wellbore or any adjacent subterranean formation. Non-limiting examples of treatments include fluid-loss control, isolation, stimulation, or conformance control.
Additionally, achieving a viscosity increase in a base liquid, usually water, is often useful in oil and gas production and recovery by way of a well. This is usually brought about by adding a viscosity-increasing agent to the base liquid or by emulsification. Increased viscosity prevents particulates with a different specific gravity than an external phase of the fluid system from quickly separating out of the external phase. Water-soluble polysaccharides and derivatives such as guar, cellulose, xanthan, scleroglucan, and their derivatives, when added can exist in a non-crosslinked or crosslinked form, and in the latter case can form a gel with the whole fluid; as a class of useful viscosity-increasing agents, they can improve the ability of the fluid system to suspend and carry particulate material, but can also be used for other purposes as, for example, friction reducers. It is to be noted that the flow of substances that have a complex structure, such as muds, sludges, suspensions, gels, etc., cannot be characterized by a single value of viscosity, which varies with temperature, pressure, and other factors. Altering—increasing, or in some instances “breaking”—the viscosity is often carried out for drilling and completion fluids, but can or can not be required or desirable for fluids used in particular treatment operations.